It has been proposed in laying railroad rails that they be fixed in place on the ties while the rail is at a preselected temperature. Proper selection of this temperature permits control of the stress of the fixed rail at the various temperatures to which it is subject. The advent of continuous welded rails (commonly called ribbon rail) has complicated the performance of this method. Welded rails are made of sections about 1400 feet in length which are transported to the site of the laying operation where they are unloaded and preliminarly placed upright on the tie plates. Even this preliminary placement introduces stress in the rail and this stress is not uniformly distributed. The individual sections weigh on the order of 35 tons and obviously are not easily moved. The end of the rail to be laid is connected to the end of an already laid rail and to the tie plates adjacent to that end. A portion of the new rail is then heated or cooled to a selected temperature by heat exchange means which traverses the rail. As the heat exchange means moves toward the free end of the rail, the portion of the rail over which it has just passed is fastened into place on the tie plates and to the ties, and anchors are applied. Experience with rails laid in this manner has been unsatisfactory. During the first winter of service, rail movement was noted. Such movement is particularly apparent at joints between rail sections where gaps developed.
Applicants concluded that the rail's length had not reached the stress free length that it would have at the temperature produced by the heat exchange, and had been fastened in place under stress and that this stress was not uniformly distributed. This conclusion is supported by observation of rail's behavior during laying with temperature adjustment. The rail's movement due to the change in length of the section undergoing temperature adjustment is not uniform. The movement is uneven and even sudden or spasmodic. This led to the conclusion that the expansion or contractin of the section being adjusted was being prevented by the friction between the base of the rail and the tie plates and by cocked tie plates. When the accumulated stress becomes large enough to overcome the friction, the spasmodic movement will occur. It was found that the rail could be caused to move somewhat sooner by striking it with a sledge hammer. It was also observed that the movement seems to occur more freely when pneumatic spike hammers were used cose to the heat exchange means.
Applicants surmised from their observations and experience that the rail could be freed so as to permit the adjusted section to change its length more freely by subjecting it to vibration. Thus they caused some rail to be laid while subject to the combined effects of heat exchange and vibration. A much more uniform accomodating movement was observed. Rail so laid was checked throughout the following winter. Each joint was examined each week throughout the winter and at what appeared to be the high and low temperatures of the week. The rail movement was markedly less and only in isolated cases was it so extreme as to cause contact between the bolts and the bolt holes at the joints. The successful results of their experimental endeavor has lead to the development of an improved vibrator described and claimed in the application of M. E. Bryne, filed on Jan. 3, 1972 under Ser. No. 214,756 now U.S. Pat. No. 3,768,859, confirmed applicants' conception of this method of laying railroad track.